Ganymede, the third
moon from Jupiter and the largest planetary satellite in the solar
system
Credit: NASA/JP

The solar system's largest moon shows
signs of what could be electric scarring. Is plasma discharge
responsible for the topography we see?

Jupiter and its moons have been the destination of several remote
observation platforms launched over the last three decades.
Beginning with Pioneer 10 in 1973 and including the most recent
visit by New Horizons this year, seven different camera packages
have flown past the planet and many of its moons.

Of all the moons,
Ganymede is possibly the most exotic, with a wild mix
(below image 1) of topography,
fractures (below image 2), craters (below image 3) and sinuous rilles
(below image 4).

Image 1

Image 2

Image 3

Image 4

Ganymede is unique among moons in that it
has a magnetic field
surrounding it, something even Mars does not possess. In December
1995, the Galileo spacecraft entered orbit around Jupiter.

During a
flyby of Ganymede at an altitude of only 838 kilometers, Galileo
discovered a dipole magnetic field very much like the one
surrounding Earth.

As with Io, the signature of Ganymede's flux
tube, the electric current that connects it with Jupiter, can be
seen in the aurora at the poles (below image).

With a mean diameter of 5262 kilometers, Ganymede
(image above) is the largest
moon orbiting any planet and is the fourth largest rocky object
after the planet Mars.

The magnetic field is supposedly being
created by the moon's core in a "dynamo" of sorts - once again like
the Earth's core is supposed to be generating its magnetic field.
There is an ambiguity, however.

Ganymede's core is too hot to hold
on to permanent magnetism. But Ganymede is so small that, according
to conventional astro-geology, it should have cooled off billions of
years ago and should not have a liquid core in the first place.

The ad hoc explanation that NASA scientists have announced creates
its own conundrum, though.

The moon once may have been much closer to Jupiter, so it was
alternately compressed and stretched by the tidal forces of the
planet's gravitational field. The constant kneading of the moon kept
its core liquid for much longer than if it had formed in its present
orbit.

If that were the case, then,

What forced an object bigger than
the planet Mercury to move into a new orbit?

Was any thought given
to a mechanism for moving several quintillion tons of rock and ice a
few thousand kilometers against the force of Jupiter's gravity?

Of course, the most obvious aspect of Ganymede's bizarre nature is
its surface (above image) and the manifold examples of apparent electric discharge
machining (EDM).

Another likely example
of EDM is the huge circular structure (below image) dominating an entire
hemisphere.

Within the darkened circle, several bright craters are
arrayed in a spiral shape that gradually decreases in diameter
toward the center. Some craters have rays (below image 5) extending outward for
several kilometers in all directions.

Several have one or more
nested concentrically (below image 6) within the other.

image 5
image 6

Such features require a
chain of unlikely coincidences if mechanical impacts are to explain
them, but EDM creates such scars naturally.

Could the magnetic field of Ganymede be related to the electrical
phenomena (below Image) that have scarred and transmogrified it?

If Ganymede was
indeed closer to Jupiter at some point in its past and was then
wrenched from orbit and thrown thousands of kilometers further out
from the tidal grasp of its parent, could the force that was
responsible for that event have been electrical in nature?

Was the
moon gripped by an electrodynamic field large enough to imprint its
core with permanent magnetism?

What effect does the electrical
connection with Jupiter have on Ganymede today?

NASA plans more missions to the moons of Jupiter in the next ten
years.

As more data is returned from a growing number of deep space
probes, perhaps the evidence for electric effects will help to
increase awareness for electricity in space.